Make discovery module compatible to Checkmk 2.4.0.

[lgetwan]

Pull request type

Please check the type of change your PR introduces:

• Bugfix
• Feature
• Code style update (formatting, renaming)
• Refactoring (no functional changes, no API changes)
• Build related changes
• Documentation content changes
• Other (please describe):

What is the current behavior?

Issue Number: #709

What is the new behavior?

• In versions 2.4.0 and newer, the modes tabula_rasa and refresh are no longer available,
  in that case, we perform a add/remove all services and labels, instead.

Other information

The API parameter mode is gone for the bulk discovery endpoint in Checkmk 2.4.0. In 2.3.0 it was already deprecated. Instead, the parameter "mode" was introduced. Thus, we use this mapping:

State	monitor_undecided_services	remove_vanished_services	update_service_labels	update_host_labels
new	X			X
fix_all	X	X		X
monitor_undecided_services	X
refresh	X	X	X	X
tabula_rasa	X	X	X	X
only_service_labels			X
only_host_labels				X
remove		X